Fly high, have the kit (dinghy, lifejacket, ELT, radio/gps in waterproof holder and from about November to June an immersion suit), know how to ditch and how to get out of the plane. Above all get taught how to survive in water. Without protection you have about half an hour in the water in March in the Channel (when the wter is coldest)
The following link may be useful
http://www.equipped.com/ditchingmyths.htm